The part of the brain that controls respiration, heartbeat, and peristalsis is the A. Medulla oblongata. The medulla oblongata is located in the lower part of the brainstem and is responsible for regulating various involuntary functions of the body, including controlling vital processes like breathing, heart rate, and digestion. It plays a crucial role in maintaining homeostasis and ensuring the body functions properly. The pons, cerebrum, and cerebellum are also important parts of the brain, but they do not directly control these specific functions.